This invention relates in general to vehicle hydraulic brake systems and in particular to a dual circuit master cylinder adapted for use in such a vehicle hydraulic brake systems.
Most vehicles are equipped with a brake system for retarding or stopping movement of the vehicle in a controlled manner. A typical brake system for an automatic or light truck includes a disc brake assembly for each of the front wheel of the vehicle, and either a disc or drum brake assembly for each of the rear wheels of the vehicle. The brake assemblies are actuated by hydraulic pressure generated when an operator of the vehicle depresses a brake pedal. A typical hydraulic brake system includes a first hydraulic circuit and a second hydraulic circuit. The first and second circuits can be connected to the wheel brakes by various configurations, such as a diagonally split arrangement or a vertically split arrangement. In a diagonally split arrangement, the first circuit is connected to one of the front wheel brakes and to one of the rear wheel brakes on the opposite side from the connected front wheel brake. The second circuit is then connected to the other one of the front wheel brakes and the other one of the rear wheel brakes on the opposite side of the connected front wheel brake. In a vertically split arrangement, the first circuit is connected to the front wheel brakes, and the second circuit is connected to the rear wheel brakes. The use of two brake circuits helps to maintain a source for braking of the vehicle in case of failure of one of the brake circuits.
A dual circuit or tandem master cylinder is used to supply pressurized fluid to the first and second brake circuits. A conventional tandem master cylinder includes a pair of service pistons which are operatively connected to the brake pedal operated by the vehicle operator. Actuation of the brake pedal causes movement of the pistons which energize or pressurize first and second fluid chambers in the master cylinder which are operatively connected in fluid communication with the first and second brake circuits, respectively. However, the use of a master cylinder having two pistons can have drawbacks should one of the two hydraulic brake circuits fail. For example, upon failure of one of the two brake circuits, the stroke of the associated piston of the master cylinder can increase in length due to abnormal movement of the associated piston, thereby causing a relatively large brake pedal drop.
It is known to use a master cylinder having a single service piston. In a master cylinder having a single piston, the movement of the piston simultaneously energizes the first and second fluid chambers. However, the respective pressures within the first and second hydraulic circuits can fluctuate with respect to each other because of different volumetric requirements of the associated hydraulic circuits due to various factors. For example, the fluctuations can result from different manufacturing tolerances, uneven brake pad or lining wear, or differences in the various components in the disc and drum hydraulic brake circuits.
It would be desirable to provide a compensation device for a master cylinder having a single service piston for use in a hydraulic brake circuit which is simple, inexpensive to manufacture, and does not cause a relatively large pedal drop in case of failure of one of the two hydraulic circuits.